The invention relates generally to articles that are used in packaging oxygen sensitive materials, and more particularly to the triggering of an oxygen scavenging composition.
Reducing the exposure to oxygen of oxygen sensitive articles maintains and enhances the quality and shelf life of the article. For instance, reducing the oxygen exposure of oxygen sensitive food products in a packaging system maintains the quality of the food product and avoids food spoilage. Reduced oxygen exposure keeps the product in inventory longer, thereby reducing costs incurred from waste and having to restock.
One method of reducing oxygen exposure is to incorporate an oxygen scavenger into the packaging structure. Oxygen scavenging compositions are compositions that consume, deplete, or reduce the amount of oxygen in a given environment. There are a wide variety of different compositions that can be used in oxygen scavenging applications. Exemplary compositions are described in U.S. Pat. Nos. 5,211,875; 5,350,622; 5,399,289; and 5,811,027 to Speer et al. and WO 99/48963 to Cai et al. The oxygen scavenging composition can comprise a substituted or unsubstituted ethylenically unsaturated composition that is capable of scavenging oxygen upon activation or triggering. The oxygen scavenging composition can also include a metal catalyst and photoinitiators that help activate oxygen scavenging, and can be “triggered” by exposing the composition to a radiation source, such as actinic radiation, having sufficient power for a sufficient amount of time to initiate oxygen scavenging. High temperatures can also help trigger the oxygen scavenging composition.
Methods of triggering oxygen scavenging compositions typically use low-pressure mercury germicidal lamps that have an intensity output from about 5 to 10 mW/cm2. These lamps are commonly referred to as germicidal since the principal emission is at 254 nm. During UV light exposure, the compositions can also be heated to further enhance triggering. Heating the composition makes it possible to trigger the oxygen scavenging composition at a lower UV dose.
Low-pressure mercury germicidal lamps have optimal performance at temperatures slightly above room temperature to slightly below room temperature. A disadvantage for triggering oxygen scavenging film that is associated with standard mercury germicidal lamps is their sensitivity to heat. As lamp temperature increases above room temperature the lamp output drops. As a result, a lamp that can be capable of an intensity of about 10 mW/cm2 at room temperature may have an intensity that is about 4 to 6 mW/cm2 at higher operating temperatures. As a practical limitation then, a balance must be struck between warming the film to facilitate triggering and the associated loss in lamp output.
The need to compensate for reduced lamp intensities at higher film temperatures results in a compromise between maximizing lamp intensity and the amount of heat that can be applied to the composition. Reduced lamp intensities can require the composition to be exposed to the lamps for a longer duration or require that a larger number of lamps be used. Although heating the film facilitates triggering, heating the film can also increase lamp temperatures, and thereby further lower intensities. At higher temperatures, a film can curl and become unusable. Current methods are typically limited to a temperature threshold that is below 50° C.
The compromise between lamp intensity and temperature can limit the speed at which the composition can be adequately triggered. Film triggering is limited to about 20 ft/min (fpm) with current methods when using as many as 80 (24 watt) germicidal lamps.